Continuous variable transmission (CVT) is an environmentally friendly automatic type transmission that can be used in different industries including automotive applications. Different types of CVT including friction type, hydrostatic type and ratcheting type CVT were developed to continuously vary the transmission ratio. In vehicles with automatic transmission, CVT enables automatic selection of optimal gear ratio that is needed according to the speed of the vehicle.
In order to provide an infinitely variable transmission, various traction roller transmissions have been developed for transfer of power through traction rollers. In such transmissions, the traction rollers are mounted on support structures which, when pivoted, cause the engagement of traction rollers with the torque discs in circles of varying diameters depending on the desired transmission ratio.
Continuously Variable Transmissions (CVT's) can provide a greater number of potential gear ratios, and in theory can continuously vary the gear ratios within the operating range of a particular CVT design. But CVT's require specially curved surfaces, such as spherical surfaces or torroidal surfaces which are not only expensive to make, but also results in concentrated forces that often lead to premature wear. Existing devices for transmission require a slip start element such as a torque converter or a friction clutch. Furthermore, friction elements are prone to increased stress and comprises a large structural assembly containing a number of components.
Therefore there still exists a need for a compact and efficient rotary power transmitting device for continuously variable transmission with reduced stress on friction elements.